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. 2023 Dec 30;29(1):219.
doi: 10.3390/molecules29010219.

Study on the Relationship between the Structure and Pyrolysis Characteristics of Lignin Isolated from Eucalyptus, Pine, and Rice Straw through the Use of Deep Eutectic Solvent

Tengfei Li  1 , Xin Jin  1 , Xinyao Shen  1 , Hangdan Liu  1 , Ruiping Tong  1 , Xuzhen Qiu  1 , Junfei Xu  1
Affiliations

Study on the Relationship between the Structure and Pyrolysis Characteristics of Lignin Isolated from Eucalyptus, Pine, and Rice Straw through the Use of Deep Eutectic Solvent

Tengfei Li et al. Molecules. .

Abstract

Understanding the pyrolysis product distributions of deep eutectic solvent (DES)-isolated lignins (DESLs) from different types of biomass is of great significance for lignin valorization. The structure and pyrolysis properties of DESLs obtained from eucalyptus (E-DESL), pine (P-DESL), and rice straw (R-DESL) were studied through the use of various methods such as elemental analysis, GPC, HS-GC, and NMR techniques, and the pyrolysis characteristics and product distributions of the DESLs were also further investigated through the use of TGA, Py-GC/MS, and tubular furnace pyrolysis. DESLs with high purity (88.5-92.7%) can be efficiently separated from biomass while cellulose is retained. E-DESL has a relatively low molecular weight, and P-DESL has a relatively higher hydrogen-carbon effective ratio and a lower number of condensation structures. The Py-GC/MS results show that, during DESL pyrolysis, the monomeric aromatic hydrocarbons, p-hydroxyphenyl-type phenols, and catechol-type phenols are gradually released when the guaiacyl-type phenols and syringyl-type phenols decrease with the rising temperature. 4-methylguaiacol and 4-methylcatechol, derived from the guaiacyl-type structural units, are positively correlated with temperature, which causes a significant increase in products with a side-chain carbon number of 1 from P-DESL pyrolysis. 4-vinylphenol, as a representative product of the R-DESL, derived from p-hydroxyphenyl-type structural units, also gradually increased. In addition, the P-DESL produces more bio-oil during pyrolysis, while gases have the highest distribution in E-DESL pyrolysis. It is of great significance to study the characteristic product distribution of lignin isolated through the use of DES for lignin directional conversion into specific high-value aromatic compounds.

Keywords: deep eutectic solvent; lignin; molecular structure; phenolic compounds; pyrolysis.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
The 2D 13C-1H (HSQC) spectra of the DESLs, and the chemical structure corresponding to each spectral peak.
Figure 2
Figure 2
Curves of TGA and DTG for the different DESLs.
Figure 3
Figure 3
Product distributions from the E-DESL, P-DESL, and R-DESL pyrolysis at different temperatures. (a): E-DESL pyrolysis products; (b): P-DESL pyrolysis products; (c): R-DESL pyrolysis products. G-phenols: guaiacyl-type phenols; S-phenols: syringyl-type phenols; H-phenols: p-hydroxyphenyl-type phenols; C-phenols: catechol-type phenols; MAHs: monomeric aromatic hydrocarbons.
Figure 4
Figure 4
The distributions of the main products from E-DESL, P-DESL, and R-DESL pyrolysis at different temperatures. (a) E-DESL pyrolysis products; (b) P-DESL pyrolysis products; (c) R-DESL pyrolysis products.
Figure 5
Figure 5
The carbon distribution of products from E-DESL, P-DESL and R-DESL pyrolysis under different temperatures.
Figure 6
Figure 6
The carbon number distributions of the longest side-chain of products from E-DESL, P-DESL, and R-DESL pyrolysis under different temperatures.
Figure 7
Figure 7
The yield of three-phase pyrolysis products from E-DESL, P-DESL, and R-DESL pyrolysis at different temperatures.
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